Enzyme Inhibition Calculator Formula

Understand the math behind the enzyme inhibition calculator. Each variable explained with a worked example.

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Formulas Used

Apparent Km (Competitive)

km_app_comp = km * alpha

Velocity (Competitive Inhibition)

v_competitive = vmax * substrate / (km * alpha + substrate)

Velocity (Noncompetitive Inhibition)

v_noncompetitive = vmax / alpha * substrate / (km + substrate)

Variables

VariableDescriptionDefault
vmaxVmax (uninhibited)(umol/min)100
kmKm (uninhibited)(uM)50
inhibitorInhibitor Concentration [I](uM)20
kiInhibition Constant (Ki)(uM)10
substrateSubstrate Concentration [S](uM)50
alphaDerived value= 1 + inhibitor / kicalculated

How It Works

Enzyme Inhibition Types

Competitive Inhibition

Inhibitor binds to the active site, increasing apparent Km while Vmax remains unchanged.

v = Vmax × [S] / (alpha × Km + [S]), where alpha = 1 + [I]/Ki

Noncompetitive Inhibition

Inhibitor binds away from the active site, decreasing apparent Vmax while Km remains unchanged.

v = (Vmax/alpha) × [S] / (Km + [S])

Competitive inhibition can be overcome by high substrate concentration; noncompetitive cannot.

Worked Example

Vmax=100, Km=50 uM, [I]=20 uM, Ki=10 uM, [S]=50 uM.

vmax = 100km = 50inhibitor = 20ki = 10substrate = 50
  1. 01alpha = 1 + 20/10 = 3.0
  2. 02Competitive: v = 100 × 50 / (50 × 3 + 50) = 5000 / 200 = 25.0 umol/min
  3. 03Noncompetitive: v = (100/3) × 50 / (50 + 50) = 33.33 × 0.5 = 16.67 umol/min

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